Instead of turning down the brightness on your handset, which still leaves a white glare searing into your retinas, try inverting the colors when you need to do some reading in the dark. Go to Settings > General > Accessibility > then toggle on Invert Colors. This flips your screen's whites to blacks, and so on. Or, you can also try switching on grayscale (located in the same settings menu) to help alleviate eye strain.